feat: Planungs- und Szenario-API mit Projektion und Vorschlaegen

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

finance/tests/test_planning_api.py

@@ -0,0 +1,47 @@
+from datetime import date
+from decimal import Decimal
+
+from app.models.tables import Account, Statement
+
+H = {"Authorization": "Bearer test-key"}
+
+
+def _seed_balance(db, amount="1000.00"):
+    acc = Account(bank="dkb", iban="DE01", name="G", type="giro")
+    db.add(acc)
+    db.flush()
+    db.add(Statement(filename="s.pdf", bank="dkb", account_id=acc.id,
+                     period_start=date(2026, 6, 1), period_end=date(2026, 6, 30),
+                     opening_balance=Decimal("0"), closing_balance=Decimal(amount),
+                     status="confirmed"))
+    db.commit()
+
+
+def test_scenario_projection(client, db):
+    _seed_balance(db)
+    client.post("/api/recurring", headers=H, json={
+        "name": "Miete", "amount": "-600.00", "rhythm": "monthly", "due_day": 1})
+    sc = client.post("/api/scenarios", headers=H, json={"name": "Basis"}).json()
+    r = client.post(f"/api/scenarios/{sc['id']}/project", headers=H,
+                    params={"horizon_days": 92, "start_date": "2026-07-15"})
+    assert r.status_code == 200
+    body = r.json()
+    # 3 Mietzahlungen (01.08., 01.09., 01.10.): 400 -> -200 -> -800
+    assert Decimal(body["low_point_balance"]) == Decimal("-800.00")
+    assert body["below_zero_date"] == "2026-09-01"
+    assert len(body["series"]) == 92
+
+
+def test_loan_in_scenario_keeps_balance_positive(client, db):
+    _seed_balance(db)
+    client.post("/api/recurring", headers=H, json={
+        "name": "Miete", "amount": "-600.00", "rhythm": "monthly", "due_day": 1})
+    loan = client.post("/api/loans", headers=H, json={
+        "name": "K1", "principal": "5000.00", "annual_rate_pct": "6.0",
+        "term_months": 48, "payout_date": "2026-07-20",
+        "repayment_type": "annuity"}).json()
+    sc = client.post("/api/scenarios", headers=H, json={"name": "Kredit"}).json()
+    client.post(f"/api/scenarios/{sc['id']}/loans/{loan['id']}", headers=H)
+    body = client.post(f"/api/scenarios/{sc['id']}/project", headers=H,
+                       params={"horizon_days": 92, "start_date": "2026-07-15"}).json()
+    assert Decimal(body["low_point_balance"]) > Decimal("0")